I. Field of the Invention
The present invention relates generally to semiconductor die packaging. More particularly, the present invention relates to an adhesive system and method for encapsulation of a die attached to a circuit board.
II. Description of the Related Art
A board-on-chip (BOC) is a semiconductor integrated circuit (IC) device where the die and the circuit board are attached and encapsulated as one package. The die and board are typically attached, prior to encapsulation, by double sided adhesive tape applied to the bottom of the board and top of the die. The die is also electrically connected to the board by wirebonds. The then attached die and board are completely encapsulated (packaged) for protection with a compound, such as plastic. The compound is injected into a mold and onto the die and board at a high pressure in a hot molten liquid form. The compound then cools and hardens to form a protective package. The encapsulation process is complex because a desired exterior surface of the board, containing the ball grid arrays (BGA), must only be partially sealed with the compound used for encapsulation. In particular, the wirebonds on the exterior surface of the board must be sealed with the encapsulating compound but the compound cannot contact the ball grid arrays. If the compound contacts the balls of a ball grid array the device will be damaged because the connectivity of the board to external circuits will be negatively effected.
FIGS. 1(a)-1(c) illustrate a conventional BOC package 100 with FIG. 1(a) showing a side view. In a conventional BOC package 100, the board 102 is physically attached to the die 104 by two pieces of double sided adhesive tape 106, 108 placed in between the die 104 and board 102. The die 104 is electrically connected to the board 102 by wirebonds 110 which pass through a wirebond slot 112 in board 102. The wirebonds 110 are all physically located between the two pieces of adhesive tape 106, 108 in the wirebond slot 112.
During encapsulation the compound must fill the wirebond slot 112 and cover all wirebonds 110 on the board 102, but the compound must not flow beyond the edges of the ball grid arrays 114, 116. FIG. 1(b) illustrates a top view of the conventional BOC package 100 and provides a clear depiction of the ball grid arrays 118, 122, the edges of the ball grid arrays 114, 116, and the wirebond slot 112.
FIG. 1(c) illustrates a cross sectional view of the BOC package along line Axe2x80x94A of FIG. 1(a) (the area between the die 104 and board 102). Referring to FIG. 1(c), during encapsulation the compound is introduce into the BOC package under high pressure at the gate 120. The compound then begins to fill a mold containing the die 104 and encapsulates the BOC package 100 in the direction of arrows 140-148. In this conventional BOC package 100 the wirebond slot 112 may fill before the compound has completely encapsulated the entire die 104. Thus, the compound may begin to flow up and over the top of the board 102 and past the edges of the ball grid arrays 114, 116 before the die 104 is encapsulated. As described above, when the compound contacts the ball grid arrays 118, 122 the BOC package will be damaged.
The foregoing problems of encapsulation of a BOC package are undesirable aspects of conventional semiconductor packaging techniques. A system and method are needed to better encapsulate a BOC package such that the ball grid array will not be damaged during encapsulation.
The present invention provides an efficient adhesive tape system and method for a BOC package which allows for better encapsulation. The present invention adds a small piece of material, for example, adhesive tape, oriented perpendicular to the conventional two-piece tape system used to attached a die to a circuit board. The material is located in front of the gate of the BOC package during encapsulation to form a diversion dam thereby causing a compound during encapsulation to fill the wirebond slot last. By filling the wirebond slot last, the present invention prevents overflow of the compound, thus ensuring that the ball grid arrays will not be damaged.